We propose to investigate why mature retinal ganglion cells (RGCs) fail to regenerate their axons after injury or in degenerative disease. Mature RGCs fail to regrow their axons once severed, yet axons in the embryonic CNS can regenerate after injury. The loss of this embryonic regenerative ability correlates with the developmental loss of RGCs' intrinsic ability to rapidly extend axons in vitro and in vivo. Interestingly, neonatal RGCs are signaled to decrease their intrinsic axon growth ability by amacrine cells, and at the same time, RGCs increase in their intrinsic ability to elongate dendrites. This switch in intrinsic regenerative ability is dependent on new gene expression, but the molecular basis is currently unknown. This is the first concrete demonstration that an intrinsic mechanism may limit regeneration. In this proposal we will use new, high-throughput technology to investigate the molecular mechanism for this loss of intrinsic axon growth ability. In the first aim we will use microarrays and methods to purify and culture RGCs and amacrine cells to broadly identify genes that RGCs change through development from embryo to early adult, and identify the subset of genes that RGCs change in response to contact with amacrine cells. In the second aim we will use powerful transfection and RNAi techniques as well as a new high-throughput imaging/analysis technology to screen the candidate genes identified in the first aim, to investigate the molecular basis of RGCs' decreased axon and increased dendrite growth abilities. This will be the first use of micro arrays to globally assay a purified neuron's gene expression through development, but with the added significance of using the candidate genes to screen for specific axon and dendrite growth phenotypes. Our goal is to revert mature, postnatal RGCs to their embryonic axon growth ability, and thereby to develop new treatments to promote RGC regeneration after injury in ocular diseases including glaucoma, retinal ischemia, optic neuritis and optic neuropathies. [unreadable] [unreadable] [unreadable]